Method for producing hyperthermal hydrogen molecules and using same for selectively breaking C—H and/or Si—H bonds of molecules at or on substrate surfaces

Abstract

A method for producing hyperthermal molecular hydrogen is disclosed and use of same for selectively breaking C—H or Si—H bonds without breaking other bonds are disclosed. A hydrogen plasma is maintained and protons are extracted with an electric field to accelerate them to an appropriate kinetic energy. The protons enter into a drift zone to collide with molecular hydrogen in gas phase. The cascades of collisions produce a high flux of hyperthermal molecular hydrogen with a flux many times larger than the flux of protons extracted from the hydrogen plasma. The nominal flux ratio of hyperthermal molecular hydrogen to proton is controlled by the hydrogen pressure in the drift zone, and by the length of the drift zone. The extraction energy of the protons is shared by these hyperthermal molecules so that average energy of the hyperthermal molecular hydrogen is controlled by extraction energy of the protons and the nominal flux ratio. Since the hyperthermal molecular hydrogen projectiles do not carry any electrical charge, the flux of hyperthermal hydrogen can be used to engineer surface modification of both electrical insulating products and conductive products. When this method of generating a high flux of hyperthermal molecular hydrogen is applied to bombard organic precursor molecules (or silicone, or silane molecules) with desirable chemical functionality/functionalities on a substrate, the C—H or Si—H bonds are thus cleaved preferentially due to the kinematic selectivity of energy deposition from the hyperthermal hydrogen projectiles to the hydrogen atoms in the precursor molecules. The induced cross-linking reactions produce a stable molecular layer having a controllable degree of cross-linking and retaining the desirable chemical functionality/functionalities of the precursor molecules.

What is claimed is: 
     
       1. A method for producing a neutral molecular hydrogen flux directed to a substrate surface, comprising the steps of:
 a) forming a plasma and extracting from said plasma a flux of protons having energies in a range from about 50 eV to about 1 keV; thereafter 
 b) directing said flux of protons into a chamber and introducing molecules of hydrogen into the chamber; 
 c) imparting kinetic energy to said molecules of hydrogen by colliding the protons from said flux of protons with the molecules of hydrogen to produce energetic hydrogen molecules; and 
 d) producing a high flux of neutral molecular hydrogen, greater than the flux of protons, having kinetic energies in a range from about 1 eV to about 100 eV by cascading collisions between said energetic hydrogen molecules and other hydrogen molecules resulting in all directional scattering of the energetic hydrogen molecules; and 
 e) directing the high flux of neutral molecular hydrogen towards the surface. 
 
     
     
       2. The method according to  claim 1  wherein said flux of protons is introduced into said chamber at one end thereof and wherein said molecules of hydrogen are introduced into said chamber at a position spaced from said one end thereof. 
     
     
       3. The method according to  claim 1  wherein a density of said flux of neutral molecular hydrogen is controlled by maintaining a pressure of said molecular hydrogen in a selected range such that said energetic molecules of hydrogen that have acquired energy from said protons undergo a pre-selected average number of collisions with other hydrogen molecules. 
     
     
       4. A method for selectively breaking any one or combination C—H and Si—H molecular bonds in molecules at or on a surface of a substrate, comprising the steps of:
 A) forming a plasma and extracting from said plasma a flux of protons having energies in a range from about 50 eV to about 1 keV; thereafter 
 B) directing said flux of protons into a chamber and introducing molecules of hydrogen into the chamber; 
 C) imparting kinetic energy to said molecules of hydrogen by colliding the protons from said flux of protons with the molecules of hydrogen to produce energetic hydrogen molecules; 
 D) producing a flux of neutral molecular hydrogen having kinetic energies in a range from about 1 eV to about 100 eV by cascading collisions between said energetic hydrogen molecules and other hydrogen molecules resulting in all directional scattering of the energetic hydrogen molecules; and 
 E) directing the flux of neutral molecular hydrogen to the substrate surface such that upon impact of neutral hydrogen molecules on molecules at or on the surface containing any one or combination of C—H bonds and Si—H bonds the C—H bonds and Si—H bonds are selectively ruptured. 
 
     
     
       5. The method according to  claim 4  wherein said flux of protons is introduced into said chamber at one end thereof and wherein said hydrogen molecules are introduced into said chamber at a position spaced from said one end thereof. 
     
     
       6. The method according to  claim 4  wherein a density of said flux of neutral hydrogen molecules is controlled by maintaining a pressure of said hydrogen molecules in a selected range such that said hydrogen molecules that have acquired energy from said protons undergo a pre-selected average number of multiple collisions with other hydrogen molecules. 
     
     
       7. The method according to  claim 4 , wherein said range of average kinetic energy of hydrogen molecules is from about 1 eV to about 20 eV. 
     
     
       8. The method according to  claim 4  wherein the substrate is selected from the group consisting of polymers, electrically insulating materials, electrically semiconducting materials, and electrically conducting materials. 
     
     
       9. The method according to  claim 4  wherein said molecules at or on the substrate surface containing any one or combination of C—H bonds and Si—H bonds are polymer-forming molecules deposited in a layer on said substrate surface. 
     
     
       10. The method according to  claim 9  wherein the deposited layer containing polymer-forming molecules has a thickness which ranges from an atomic monolayer to more than 100 nm. 
     
     
       11. The method according to  claim 9  wherein the polymer-forming molecules comprise saturated or unsaturated organic molecules. 
     
     
       12. The method according to  claim 9  wherein the polymer-forming molecules comprise saturated or unsaturated organic molecules with chemical functional groups. 
     
     
       13. The method according to  claim 9  wherein the polymer-forming molecules comprise saturated or unsaturated silanes and their derivatives. 
     
     
       14. The method according to  claim 4  wherein said molecules at or on the substrate surface containing any one or combination of C—H bonds and Si—H bonds are molecules forming part of the substrate itself. 
     
     
       15. The method according to  claim 4  wherein said molecules at or on the substrate surface containing any one or combination of C—H bonds and Si—H bonds is a combination of molecules forming part of the substrate itself and molecules deposited on said substrate surface. 
     
     
       16. The method according to  claim 9  wherein the layer containing polymer-forming molecules is deposited using any one or combination of spraying, spin-coating, dip-casting, jet-printing, and screen-printing. 
     
     
       17. The method according to  claim 4  wherein any one or combination of ruptured C—H bonds and Si—H bonds cross-link with themselves or with other chemical moieties at said surface resulting in a change in surface properties. 
     
     
       18. The method according to  claim 17  wherein said surface properties are any one or combination of Young's modulus, hardness, ionic conductivity, electrical conductivity, surface energy, surface chemistry, friction, permeability, diffusivity, adhesion, wettability, and surface biochemical properties. 
     
     
       19. The method according to  claim 17  wherein a degree of said change in said surface properties is controlled by controlling any one or combination of the energy and fluence of said neutral molecular hydrogen molecules hitting said substrate surface, and the molecules at or on said substrate surface. 
     
     
       20. The method according to  claim 17 , including introducing pre-selected molecules into said chamber while simultaneously directing the flux of neutral molecular hydrogen to the substrate surface to induce cross linking of the ruptured C—H and/or Si—H bonds with said pre-selected molecules for altering a chemical composition of the surface compared to the rest of the substrate. 
     
     
       21. The method according to  claim 4  including applying any one or both of a positive direct-current and an alternating-current electrical bias to said substrate during bombardment of the substrate by the neutral molecular hydrogen. 
     
     
       22. The method according to  claim 4  including applying any one or both of a negative direct-current and an alternating-current electrical bias to said substrate during bombardment of the substrate by the neutral molecular hydrogen. 
     
     
       23. The method according to  claim 1  wherein the flux of neutral molecular hydrogen has kinetic energies in a range of from about 1 eV to about 20 eV.